The incandescent light bulb is commonly found in a bulbous, pear-shaped configuration. The pear-shaped configuration is popularly referred to by the American National Standards Institute (ANSI) as the “A” shape.
The “A” terminology carries with it a numerical reference following the “A,” such as “A19.” The numerical reference following the “A” represents the widest part of the lamp envelope, in units of ⅛ (0.125) of an inch. Thus, an incandescent bulb described as “A19” indicates that the widest part of the lamp envelope is (19×0.0125), or 2.375 inches in diameter. The overall length of the A19 form factor is 4.25 inches. A19 incandescent bulbs are frequently designed to use 45, 60, 75, or 100 Watts (W) of energy.
LEDs have been used for decades in applications requiring relatively low-energy indicator lamps, numerical readouts, and the like. In recent years, however, the brightness and power of individual LEDs have increased substantially, resulting in the availability of 1 watt, 3 watt, and 5 watt devices.
While small, LEDs exhibit a high efficacy and life expectancy as compared to traditional lighting products. A typical incandescent bulb has an efficacy of 10 to 12 lumens per watt, and lasts for about 1,000 to 2,000 hours; a general fluorescent bulb has an efficacy of 40 to 80 lumens per watt, and lasts for 10,000 to 20,000 hours; a typical halogen bulb has an efficacy of 15 lumens and lasts for 2,000 to 3,000 hours. In contrast, LEDs can emit more than 100 lumens per watt with a life-expectancy of about 100,000 hours.
Thus, LED lighting sources can provide a brilliant light in many settings. LED lights are efficient, long-lasting, cost-effective, and environmentally friendly. For the above reasons, LED lighting is rapidly becoming the light source of choice in many applications.
Because of the many advantages associated with LED light sources, there remains continued interest in replacing traditional lighting products, such as incandescent and compact fluorescent (CFL) bulbs, with a corresponding LED lamp that has the same form, fit, and function. For example, for a particular lighting fixture that uses an A19 bulb, it is desirable to “swap out” a 60 W incandescent bulb with an LED lamp that emits approximately the same amount of light but has a much longer life expectancy and reduced operating cost.
The term “Energy Star” refers to the U.S. government's energy performance rating system program that is jointly managed by the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA). According to Energy Star guidelines, a 40 W incandescent bulb nominally emits 450 lumens, while a 60 W incandescent bulb nominally emits 800 lumens. Thus, to be considered a valid replacement for a 60 W incandescent bulb, an LED lamp should emit at least 800 lumens.
LED light sources rely on LED light engines to generate the light energy that is emitted from the light source. The LEDs are electrically interconnected and a power supply energizes the LEDs via connection terminals connected to the substrate.
Today, a typical efficacy for a warm (color temperature of about 2600 to 3000 degrees K) LED light engine is around 100 lumens/W. Assuming optical, thermal, and electrical losses of about 15% each, the overall efficacy for an LED lamp incorporating such an emitter is about 60 lumens/W. Thus, the LED lamp would require about 10 W to generate a light output of 600 lumens, or about 13.3 W to generate a light output of 800 lumens. If 25% of the electricity is converted to light energy and the other 75% to heat energy, the LED lamp produces about 10 W of heat energy in order to achieve an output of 800 lumens. As the above example illustrates, an LED light engine typically generates a substantial amount of heat energy.
Heat dissipation and weight are important design considerations. Heatsinks tend to be large and heavy. It is difficult to accurately control the thickness of heatsinks leading to excessive weight. Heatsinks also add substantially to the overall cost of an LED lamp.